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My Fn key doesn't seem to work/help me to adjust brightness. So I tried to minimize the brightness (inside the Control Panel). To my surprise, the screen went entirely black and I couln't see a way to cancel it. Now I can't do anything in my area, not even log on to the account (it seems). The only thing I can do is to enter Windows' Security Mode. There, I see an option to log in and I can enter a security version of my area and there I have proper brightness. If I try to enter with Windows "normal mode", I can't even see the login screen.

I tried from my account in Security Mode using powercfg and update the brightness value. However it doesn't seem to have effect on Windows' Normal Mode.

Any suggestions on what I can do?

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2 Answers 2

I figured it out. Using powercfg -l to list the current power schemes, I saw that it was using the "Power save" configuration (or whatever it is called in English, since my system is in Portuguese). In that configuration, the brightness value for AC was set to 0. There were two possible solutions, then:

  1. Increase the brightness value of this configuration, using powercfg -setacvalueindex Scheme_GUID Sub_GUID Setting_GUID SettingIndex, where SettingIndex would be something grater than zero.
  2. Set one of the other two schemes as active, using powercfg -setactive Scheme_GUID

I picked number 2.

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Try this: Login using the security mode and open command shell (cmd). Then type:

powercfg -restoredefaultschemes

Follow any instructions and then reboot.

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